Nintendo has released a new trailer showing several new highlights and features of Pokémon Omega Ruby and Alpha Sapphire.

Quote from: Nintendo Press Release

New Mega-Evolved Pokémon Mega Metagross!A new Mega-Evolved Pokémon was revealed today—Mega Metagross. Metagross is the partner Pokémon of Pokémon League Champion Steven, whose deep bond helps it to Mega Evolve into Mega Metagross. Despite helping Trainers throughout their journey, Steven is the last obstacle for Trainers to overcome before becoming the Pokémon League Champion.

Mega Metagross, the Iron Leg Pokémon, is a massive Steel- and Psychic-type Pokémon standing at 2.5 m (8’02”) and weighing 942.9 kg (2078.7 lbs). Upon Mega Evolving, Metagross’s Ability changes to Tough Claws, which increases the power of attacks that make physical contact. Mega Metagross also has a greatly increased Speed stat, with additional increases in its Attack, Defence, Sp. Atk, and Sp. Def, making Mega Metagross primed for both offence and defence.

Deepen Your Bonds with Pokémon-Amie and Meet Cosplay Pikachu!First introduced in Pokémon X and Pokémon Y, Pokémon-Amie returns in Pokémon Omega Ruby and Pokémon Alpha Sapphire. Pokémon-Amie allows Trainers to create close ties with their Pokémon by playing games together, petting them, and feeding them special snacks called Poké Puffs. As a player’s Pokémon become more affectionate, they will be more likely to do such things as evade attacks in battle, land critical hits, and get an overall boost in performance.

Players will see Pikachu like they’ve never seen it before—Cosplay Pikachu—in Pokémon Omega Ruby and Pokémon Alpha Sapphire. Meet Pikachu Rock Star, Pikachu Belle, Pikachu Pop Star, Pikachu Ph.D., and Pikachu Libre! They seem to have a connection to a kind of Contest Hall. Players will also be able to interact with Cosplay Pikachu in Pokémon-Amie. More information about the new Cosplay Pikachu images shown today will be revealed in August!

Journey through the Hoenn RegionYour Hoenn adventure begins when you meet Pokémon Professor Birch, who runs the Pokémon Lab in Littleroot Town. Professor Birch will help players begin their journey by giving them their first Pokémon and a Pokédex. The Pokémon that appear and the rarity of each will differ between Pokémon Omega Ruby and Pokémon Alpha Sapphire.

The first step to becoming the Champion is to challenge and defeat each of the Gym Leaders in the Hoenn region, including the main character’s father, Norman, who is the Leader of the Petalburg City Gym. It was also confirmed today that players will encounter and battle Rustboro City Gym Leader Roxanne, Dewford Town Gym Leader Brawly, Mauville City Gym Leader Wattson, and Lavaridge Town Gym Leader Flannery.

After defeating eight Gym Leaders, players will travel to the Pokémon League to battle the Elite Four, including Sidney and Phoebe. Upon defeating the Elite Four, Trainers will take on the Hoenn League Champion, Steven, and his Mega Metagross, in the hope of becoming the new Pokémon League Champion!

More Information on Mega Diancie Revealed!When Diancie Mega Evolves into Mega Diancie, it will get the Magic Bounce Ability, which makes any status condition or stat-lowering effect bounce back at the Pokémon trying to inflict it. Through Mega Evolution, Mega Diancie receives a big boost to its Speed, as well as boosts to its Attack and Sp. Atk, while experiencing a reduction in its Defense and Sp. Def. The boosts help Mega Diancie with its quick, powerful attacks, such as Diamond Storm and Moonblast.

Further details of how players can get Diancie for Pokémon X and Pokémon Y will be shared soon. Players who receive Diancie can Mega Evolve it in Pokémon Omega Ruby or Pokémon Alpha Sapphire.